1. Field of the Invention
This invention relates to a temperature sensing tube for an expansion valve, which senses a refrigerant temperature in an outlet of an evaporator, for example, by being attached to a piping of the evaporator, and is used for controlling a flow rate of the expansion valve on the basis of the sensed temperature, in order to control a flow rate of a refrigerant passing the expansion valve.
2. Description of the Conventional Art
In conventional, a refrigeration system is generally constructed by connecting a condenser, an evaporator and a compressor by a refrigerant piping, and a temperature expansion valve is arranged between the condenser and the evaporator. The temperature expansion valve has both a function of depressurizing a refrigerant supplied to the evaporator so as to make refrigerant evaporation within the evaporator easy and a function of controlling a flow rate of the refrigerant flowing into the evaporator. In the temperature expansion valve, a valve opening degree is controlled in accordance with feedback control by a superheat degree signal on the basis of a difference between a superheat evaporation temperature in an outlet of the evaporator and an evaporation temperature. A mechanism for converting the signal into the valve opening degree is a power element portion, evaporation pressure and force of a bias spring are applied to a lower portion of a diaphragm constructing the power element portion, and pressure of an internal gas of the temperature sensing tube which is thermally balanced with the evaporation temperature in the outlet of the evaporator is applied to an upper portion of the diaphragm.
FIG. 4 is an explanatory view showing an outline of the temperature sensing tube for controlling the temperature expansion valve in the refrigeration cycle. As shown in FIG. 4, a so-called temperature sensing tube 31 is attached so as to come into contact with a piping of the evaporator, for sensing the superheat evaporation temperature in the outlet of the evaporator. The temperature sensing tube 31 is connected to a power element portion of a temperature expansion valve 30 through a capillary tube 32. The power element portion has a well-known structure provided with a diaphragm, and gas pressure from the temperature sensing tube 31 is supplied to an upper pressure chamber of the power element portion through the capillary tube 32. Further, since a lower pressure chamber of the diaphragm communicates with a valve chamber of the temperature expansion valve 30, the diaphragm is activated by a pressure change within the pressure chamber on the basis of a temperature change of the refrigerant within the temperature sensing tube 31, and the valve opening degree of the temperature expansion valve 30 is changed, thereby controlling the flow rate.
In the refrigeration system, there is a hunting as a phenomenon which is preferably avoided. The hunting is a phenomenon that excess and short of the refrigerant supply amount to the evaporator are repeated, due to a structure of the evaporator, piping of the refrigerant circuit, a mode of use of the temperature expansion valve, a balance with a thermal load, and the like. If this phenomenon is caused, there occurs an adverse effect that a capacity of the whole of the refrigeration cycle is lowered, and a load such as returning back of liquid to the compressor or the like is increased.
As one of suppressing methods of the hunting phenomenon, there can be indicated a method of charging and sealing a thermal ballast serving as a heat transfer delaying member in an inner portion of the temperature sensing tube constructing the power element of the temperature expansion valve so as to delay a valve opening speed at a time when the superheat degree rises. As the thermal ballast, there is employed a heat insulating material having a fixed heat capacity and having a bad heat transfer, for example, a ceramic sintered material constituted by an alumina silica. Further, Japanese Unexamined Patent Publication No. 1-179871 discloses a temperature expansion valve structured such that a temperature sensing tube, in which a ceramic sintered member constituted by a silica alumina is arranged in an inner portion, is connected to a power element portion by a capillary tube.